Wake generators may be used in gas turbine research, e.g., to provide unsteady wakes representative of blade passage wakes or other wakes that may be experienced while a turbine is in use. These wakes may have an effect on the flow around turbine components, and, as such, high fidelity research aimed at evaluating unsteady effects on turbines should account for wake passage. For example, wakes can cause a fluctuating pressure distribution on turbine blades or vanes, influencing the aerodynamic qualities and the behavior of film cooling flows. As the desire grows for higher fidelity engine representative conditions that include unsteady flow effects, it is expected that more experimentalists begin incorporating wake generators into their testing facilities.
Wake generators can have cylindrical rods or other wake-producing objects that traverse upstream of a test article in a wind tunnel. The rods intersect and disrupt air flow as they traverse across the width of the wind tunnel to produce an unsteady wake that traverses across the test article. By way of example, some of the wake generators used in research include: (i) a rotating bar wake generator; (ii) a “squirrel cage” wake generator; and (iii) a traversing wake generator. These current and past wake generators are generally limited to creating a wake in a linear or rotational fashion, and include various disadvantages, where some are discussed below.
Rotating bar wake generators can be inefficient in simulating a wake inside a turbine engine (e.g., causing only a full wake at one point), can cause air leakage (e.g., if slots or the like need to be cut into the wind tunnel), can be cumbersome, and so on.
Squirrel cage wake generators may include cylindrical bars mounted axially between two parallel disks that are driven by a motor. Because of the circular path of the cylindrical bars, the velocity profiles do not precisely match those in turbine engines. Also, a secondary wake, sometimes referred to as a reverse wake, is produced when a cylinder is upstream of another cylinder, and absorbs the wake produced by the cylinder directly in front of the test piece.
Traversing wake generators may include cylindrical bars mounted on a rail where the bars pass upstream of the test article in a straight line. However, because the bars do not make a return trip to the starting point, these designs allow for only short duration testing dictated by the length of the bar cascade and the speed at which the bars translate. Also, because these designs generally involve large holes cut in a wind tunnel, air leakage can be a concern.
There remains a need for improved wind tunnel wake generators, e.g., to minimize reverse wakes and the effects thereof.